Heat treat question for Spätzle knife

[Hubert S.]

Hi, I am new here and just started making knives as a hobby. I have made a couple of knives out of 80CRV2 and learned a lot from the forums. Thank you everybody for posting so much information.

I am planning a new knife design for making Swabian spätzle and I am hoping to get some input regarding heat treating the blade. I plan to make the knife out of AEB-L and have found great info here about heat treating it. My question is more about tempering as this knife is not meant to be sharpened and should have some flex like a spatula for cake decorating. Maybe I should explain a bit how the knife will be used. Spätzle are traditionally made by scraping a noodle dough off a wooden board directly into boiling water. For scraping, either a dull knife or a special scraper is commonly used. The scraper is thin sheet metal with a rolled top for a handle. This type of scraper appears to be highly optimized for low production cost, but not really for the task at hand. The problem with the knives I have is that you end up hitting the rim of the pot either with the knife or your knuckles if you rest the wooden board on the rim of the pot. So I have sketched a knife design that gives more clearance and tested a plywood mock-up to see if it is comfortable and does not interfere with the pot. It seems to work well and I plan to make one out of 0.04" AEB-L.

My question is what temperature should I temper the blade at? Any advice would be greatly appreciated.

 

[Cushing H.]

Ive made spatzle - love the stuff! I suspect you might get a range of answers here, as what you are trying to do is exactly the opposite of what almost everyone here is aiming for (that being SHARP, and tough). I am thinking your needs actually will not suffer from the typical tradeoffs: in your case, you do not need sharp, and hence really just also do not need toughness. You do, however, want to stay as far away from brittleness as you can. That mans go as low on rockwell as is reasonable. You might also be concerned about rust resistance ... i seem to recall aebl has max rust resistance around 62 rockwell (which might be too hard for you). If you are careful about drying the thing, resistance is likely not really an issue, so i would be tempted to just go as low ij rockwell as you can. I am not even sure how low you can reasonably take aebl ... 55? (But you dont want itso low that it starts bending as you scrape it sideways....)

 

[Ken H>]

Since you're not wanting sharp, but do want flex what about tempering similar to a slipjoint backspring? That's in the 45 Rc range. HT as normal, then temper around 1100°F is what I do for backsprings and they normally turn out around 45 Rc.

 

[Willie71]

Hi, I am new here and just started making knives as a hobby. I have made a couple of knives out of 80CRV2 and learned a lot from the forums. Thank you everybody for posting so much information.

I am planning a new knife design for making Swabian spätzle and I am hoping to get some input regarding heat treating the blade. I plan to make the knife out of AEB-L and have found great info here about heat treating it. My question is more about tempering as this knife is not meant to be sharpened and should have some flex like a spatula for cake decorating. Maybe I should explain a bit how the knife will be used. Spätzle are traditionally made by scraping a noodle dough off a wooden board directly into boiling water. For scraping, either a dull knife or a special scraper is commonly used. The scraper is thin sheet metal with a rolled top for a handle. This type of scraper appears to be highly optimized for low production cost, but not really for the task at hand. The problem with the knives I have is that you end up hitting the rim of the pot either with the knife or your knuckles if you rest the wooden board on the rim of the pot. So I have sketched a knife design that gives more clearance and tested a plywood mock-up to see if it is comfortable and does not interfere with the pot. It seems to work well and I plan to make one out of 0.04" AEB-L.

My question is what temperature should I temper the blade at? Any advice would be greatly appreciated.

your hardness is relatively secondary. Higher hardness is higher strength. Flex is geometry, not hardness. I would see no need to go lower than Rc60 with AEB-l. You would be fine at the usual Rc62 as well. Going too soft might mean the thin “blade” might take a set, rather than returning to flat.

of course, I’ve never made one, so others may have much better real world experience.

 

[Cushing H.]

You would be fine at the usual Rc62 as well. Going too soft might mean the thin “blade” might take a set, rather than returning to flat.

thats what I was meaning when I said the blade might "bend" (permanently I left out.....). Do you think there is risk of that below 62? I was thinking that the higher the rockwell, the more the risk of brittle breakage. sounds like you think that is small at 62? (again, in usage, this is specifically taking a rather wide blade, and scraping is sideways, perhaps causing flexure along the long dimension......)

 

[Willie71]

thats what I was meaning when I said the blade might "bend" (permanently I left out.....). Do you think there is risk of that below 62? I was thinking that the higher the rockwell, the more the risk of brittle breakage. sounds like you think that is small at 62? (again, in usage, this is specifically taking a rather wide blade, and scraping is sideways, perhaps causing flexure along the long dimension......)

the thinner you go, the higher the hardness you need to prevent taking a set. AEB-l is one of the least brittle steels available to us, making it ideal for this application. I have never seen an AEB-l blade break at Rc62.

 

[Cushing H.]

the thinner you go, the higher the hardness you need to prevent taking a set

That makes sense .... but cant you go high (brittle) enough that you just snap the blade when bending it? I guess I am thinking that here it is better to accept some risk of permanent set than a snapped blade.... (which is why I was thinking lower hardness is better in this application???)

 

[Willie71]

That makes sense .... but cant you go high (brittle) enough that you just snap the blade when bending it? I guess I am thinking that here it is better to accept some risk of permanent set than a snapped blade.... (which is why I was thinking lower hardness is better in this application???)

go Rc60 then. I can bend my z-wear thin knives to 90deg, at Rc63, without breaking. If your blade was 1/4” thick, you would risk snapping it much more so. Thin bends easily.

 

[Ken H>]

Why do you think slipjoint backsprings are normally tempered to mid 40s Rc hardness? At least that's what I've always read, and what I do. Of course the geometry of a backspring is different than a slim thin blade.

 

[Hubert S.]

Thanks for your suggestions. What Warren said is what I vaguely remember from long ago college classes. The modulus is not changed by heat treat and therefore, the flex is only a function of geometry. But the yield strength increases with hardness and the steel might become so brittle that it fractures without yielding. Being absolutely new to this, I have no feel for how big a problem this might be, but I guess I am overanalyzing it... I will make some test coupons and try to destroy them. I did that when I made the knives from 80CRV2 and was quite surprised how much it took to snap a 2mm thick coupon straight out of the quench.

I hope to make the knife after Christmas, but it might not happen until next year. I still have to get quench plates and foil.

 

[Hubert S.]

In case somebody comes across this thread someday searching for information on how to make a knife for Spätzle, I thought I should post an update. I ended up tempering the blade at 400°F and so far so good. I will report back if there are any issues.

The knife works really well. I made about four pounds of Spätzle today and it went rather quickly. The knife works well both for managing the dough on the board and cutting the noodles. The blade is 1mm thick at the spine and has a single bevel on the right side tapering down to about 0.35mm at the edge over a distance of about 15mm. It cuts the dough nicely but does not cut into the board. Since this is only the third knife I have made and the first one on a belt grinder, the bevel started out pretty uneven. I evened out the bevel on a coarse diamond stone and then used a scotch brite belt to give it a satin finish holding the knife vertically against the platen, tilting it from flat to bevel. This makes the nice even bevel I spent fifteen minutes on with the diamond plate almost impossible to see. The dough does not stick to the satin finish any worse than it does to the polished cake frosting knife I had been using in the past.

Here is a picture of the knife on top of the maple/walnut Spätzlebrett I made around twelve years ago or so. The knife has black canvas micarta scales with garnet liners.

 

[Willie71]

In case somebody comes across this thread someday searching for information on how to make a knife for Spätzle, I thought I should post an update. I ended up tempering the blade at 400°F and so far so good. I will report back if there are any issues.

The knife works really well. I made about four pounds of Spätzle today and it went rather quickly. The knife works well both for managing the dough on the board and cutting the noodles. The blade is 1mm thick at the spine and has a single bevel on the right side tapering down to about 0.35mm at the edge over a distance of about 15mm. It cuts the dough nicely but does not cut into the board. Since this is only the third knife I have made and the first one on a belt grinder, the bevel started out pretty uneven. I evened out the bevel on a coarse diamond stone and then used a scotch brite belt to give it a satin finish holding the knife vertically against the platen, tilting it from flat to bevel. This makes the nice even bevel I spent fifteen minutes on with the diamond plate almost impossible to see. The dough does not stick to the satin finish any worse than it does to the polished cake frosting knife I had been using in the past.

Here is a picture of the knife on top of the maple/walnut Spätzlebrett I made around twelve years ago or so. The knife has black canvas micarta scales with garnet liners.

That turned out really nice. I might have to make one for my mother.

 

[Cushing H.]

Nice. Thank you for the update!